1. Field of the Invention
The present invention pertains to respiratory interface devices and, in particular, to an improved mask that is retained with improved reliability on a patient.
2. Description of the Related Art
There are numerous situations where it is necessary or desirable to deliver a flow of breathing gas non-invasively to the airway of a patient, i.e., without intubating the patient or surgically inserting a tracheal tube in their esophagus. For example, it is known to ventilate a patient using a technique known as non-invasive ventilation. It is also known to deliver continuous positive airway pressure (CPAP) or variable airway pressure, which varies with the patient's respiratory cycle, to treat a medical disorder such as sleep apnea syndrome in particular, obstructive sleep apnea (OSA), or congestive heart failure.
Non-invasive ventilation and pressure support therapies involve the placement of a respiratory patient interface device including a mask component on the face of a patient. The mask component may be, without limitation, a nasal mask that covers the patient's nose, a nasal cushion having nasal prongs that are received within the patient's nares, a nasal/oral mask that covers the nose and mouth, or full face mask that covers the patient's face. The respiratory patient interface device interfaces the ventilator or pressure support device with the airway of the patient, so that a flow of breathing gas can be delivered from the pressure/flow generating device to the airway of the patient. It is known to maintain such devices on the face of a wearer by a headgear having one or more straps adapted to fit over/around the patient's head. Because such respiratory patient interface devices are typically worn for an extended period of time, it is important for the headgear to maintain the mask component of the device in a tight enough seal against the patient's face without discomfort.
For respiratory patient interface devices, a key engineering challenge is to balance patient comfort against stability of the device. As a patient changes sleeping positions through the course of the night, the mask portions of respiratory patient interface devices may become dislodged, and the seal against the patient may be broken. A dislodged mask portion can be stabilized by the increasing strapping force provided by the headgear, but increased strapping force tends to reduce patient comfort. This design conflict is further complicated by the widely varying facial geometries that a given respiratory patient interface device design needs to accommodate.